1. Field of the Invention
The invention relates generally to gas appliance ignition systems, and more particularly to such systems in which spark ignited recycling pilots are employed. See also U.S. Pat. No. 3,832,123.
2. Description of the Prior Art
In the prior art, the problem of gas appliance ignition has been addressed variously. Until comparatively recently, most gas appliances such as furnaces, hot water heaters and cooking equipment, etc., have incorporated a continuously burning pilot flame. Such an appliance can be placed in full operation, i.e., a main burner or burners may be ignited conveniently without significant delay.
Safety and reliability have also been considered in the prior art.
Among those safety devices known and used in the prior art to prevent such events as the ignition of main burner gas when the pilot flame is not extant is the well-known pilot thermopile, "thermomag," and safety valve. In such systems, the power source for a solenoid operated main gas valve is derived from a pilot generator relying on the heat of the pilot itself. Thus, if the pilot is not burning, the main solenoid operated gas valve cannot be operated. There are, of course, a host of other arrangements addressing the same or similar problems in all branches of the gas appliance art ranging from large steam boilers on down to the smallest of household gas appliances.
More recently, concern for natural resource conservation has spawned a generation of devices for quickly and conveniently lighting gas appliances without the need for a continuously burning pilot.
One of the most promising of the new generation ignitor arrangements includes an electrical spark gap for causing gas ignition. One such device is described in U.S. Pat. No. 3,870,929 issued Mar. 11, 1975.
Many devices disclosed in the recent art, including the device described in the aforementioned U.S. Pat. No. 3,870,929, combine a spark gap ignitor with a so-called flame rod, the latter being a device known per se in boiler control and gas appliance systems generally. Briefly, the so-called flame rod is located so that the burner flame, when present, impinges at least partly upon it. The flame, when present, thus forms a "flame diode" or high resistance rectifier with the rod as the anode and the burner as the cathode. In the absence of flame the circuit between the flame rod and burner is an open circuit. With the flame impinging upon the rod, a current path having a resistance in the order of several megohms is presented. This phenomenon has been used to control safety devices to prevent the discharge or collection of unburned gas in the event that the ignition device does not operate properly for any reason. The aforementioned U.S. Pat. No. 3,870,929 illustrates and describes much of this current art.
Still more recently, spark ignitors have been applied to the ignition of a gas pilot which then ignites the main burner or burners in the well known way. The pilot flame, being a device of smaller gas utilization, does not present some of the problems which can result from delayed or inadequate ignition of a larger gas discharge. U.S. Pat. No. 3,662,185 describes the so-called flame rod in a spark ignition system. In that patent, the flame rectification or flame diode action provides an electrical inhibiting means by which the spark ignition device can be inhibited, once the pilot has ignited.
Within the current state of the art, no device is known combining the advantages of pilot spark ignition and interlocking solenoid safety valves to insure fail-safe and reliable gas appliance operation.
The use of spark igniters with gas fuel pilots presents certain unique problems in bringing about reliable and fail-safe operation and also creates certain opportunities for effecting economical and efficient electrical interlocking of the gas controls. In the prior art as in the combination of the present invention to be described hereinafter, solenoid operated gas valves are employed. Such valves are extremely well known and are extensively described in the patent literature. The art of constructing solenoid valves for gaseous or vaporous fuels and other fluids is well developed and they have been widely used in a variety of voltage and current sizes. U.S. Pat. Nos. 2,557,514; 2,589,574; 2,697,581; 2,719,939 and 2,947,510 provide but a small sampling of the art in solenoid operated valves.
The manner in which the present invention builds upon the prior art and substantially improves upon it will be evident as this description proceeds.